1. Field of the Invention
The present invention relates to a control system for an automatic transmission, and in particular to a control system for an automatic transmission which includes a combination of a main transmission and a subtransmission.
2. Description of the Prior Art
There is known an automatic transmission which combines a main transmission and a subtransmission for establishing a larger number of gear ratios. As shown in Japanese Patent Laid-Open Publication No. 62-4950, the conventional automatic transmission of this type starts the operation of changing the gear ratio in the main transmission earlier than that in the subtransmission and synchronizes the main transmission and the subtransmission at the end of the operation of changing the gear ratio, thereby preventing occurrence of shocks during the operation.
The conventional automatic transmission including the conbination of a main transmission and a subtransmission is nevertheless apt to produce shocks in the transition region of the operation of changing gear ratios. It is thus important to match the operation of the main transmission with that of the subtransmission as a whole, because shocks are produced when one of the transmissions is operated earlier than the other.